The present invention relates to a precision moving mechanism which can move an object to a desired position at high speed and with a high precision.
In recent years, apparatus for forming fine patterns on a semiconductor wafer, mask film or the like have been developed. Among these apparatus are an electron beam exposure apparatus, a reduced image projection apparatus and an X-ray image transfer apparatus. These apparatus need to have a precision moving mechanism for moving a sample (i.e., a wafer, mask film, etc.) so slightly that patterns may be drawn on the sample with a high precision of a submicron. Some of the apparatus used in other fields of art may require a precision moving mechanism.
Various precision moving mechanisms have been developed. Among these is the fine rotation mechanism disclosed in U.S. Pat. No. 4,455,501 issued June 19, 1984. This mechanism has a piezoelectric element, which expands and contracts to very slightly move a sample, requiring no complex control. It comprises a rotational table for supporting a sample, a base, and a drive disk rotatably mounted on the base. The drive disk has first and second movable sections, one of which supports the rotational table. An piezoelectric element is provided between the movable sections. First and second stoppers are provided to make the movable sections immovable with respect to the base. They are alternately driven by a stopper drive means. A voltage generator is provided to apply a voltage to the piezoelectric element, so that the element expands every time one of the stoppers is driven and contracts every time the other stopper is driven. However, the mechanism is disadvantageous in the following respect.
The table can indeed be rotated at a desired speed, but it rotates intermittently. Obviously, it takes much longer to move the sample to a desired position than when the table is continuously rotated. To move the sample more quickly, the stoppers may be driven more frequently and a voltage of a higher frequency may be applied to the piezoelectric element. The higher the frequency of the voltage, the lower is the impedance of the load circuit including this element. This is because a piezoelectric element is a capacitive load. When the impedance of the load circuit is lowered, the output impedance of the voltage generator must be proportionally lowered. However, it is difficult to design a voltage generator which can stably amplify the input AC signal and whose output impedance is low, without damaging the response of the voltage generator.